phm2213 surf act ant liquid crystal
TRANSCRIPT
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Surfactants
Introduction to Liquid Crystals
Kausar AhmadKausar Ahmad
Kulliyyah of PharmacyKulliyyah of Pharmacy
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ContentsContents
Properties of liquidProperties of liquid
crystalscrystals
Types of liquid crystalsTypes of liquid crystals
ThermotropicThermotropic
nematicnematic
smecticsmectic
cholestericcholesteric
LyotropicLyotropic
structuresstructures
applicationapplication
NIOSOMESNIOSOMES
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Synergistic Effects of Surfactants
Observed when surfactants having relatively similar
structure or ionic property are mixed
Resulted in the formation of liquid crystal structures
or complexes at the interface by intermolecular
interactions between surfactants
Examples
Anionic and nonionic in synthetic latex emulsion
polymerisation,
Mixture of a dispersant and a hydrating agent to
increase dispersion stability in agricultural chemicals
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STATES OF MATTER
Common states:
solid
liquid
gas
Matter can exist in
other states
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LIQUID CRYSTALS
A state that occurs between a solid & a liquid
Possess properties characteristics of both
liquids & crystalline solids
Also possess properties not found in either
liquids or solids
May response to external perturbations &some changes colour with temperature
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A crystal is a highly ordered structure which
possesses long-range positional & orientational
order
For many substances these two types of order are
destroyed simultaneously when the crystal melts to
form a liquid
For some substances, these orders are
destroyed in stages. These are liquid crystals.
E.g. Slide 17
Crystals vs Liquid Crystals
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Liquid crystal can flow like a liquid, due to loss of
positional order
Liquid crystal is optically birefringent, due to its
orientational order
Transition from crystalline solids to liquid crystals caused
by a change of temperature gives rise to
THERMOTROPIC liquid crystals
substances that are most likely to form a liquid crystalphase at a certain temperature are molecules that are
ELONGATED & have some degree of RIGIDITY. Try
slide 29
Properties of liquid crystals
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Typical chemical structures
cholesterol ester
phenyl benzoates
surfactants such aspolyethylene-oxides,alkali soaps, ammoniumsalts, lecithin
paraffins
glycolipids
cellulose derivatives
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Typical applications
LCD displays
dyes (cholesterics)
advanced materials (Kevlar)
membranes
temperature measurement (by changing colours)
solvents for GC, NMR, reactions, etc.
Drug delivery
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Types of liquid crystals
Thermotropic
Phase transition depends on temperature
Nematic Smectic
Cholesteric
Lyotropic
Phase transition depends on temperature &concentration
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As temperature increases..
The first liquid crystal phase is the smecticA, where there
is layer-like arrangement as well as translational and
rotational motion of the molecules.
A further increase in temperature leads to the nematicphase, where the molecules rapidly diffuse out of the initial
lattice structure and from the layer-like arrangement as well.
At the highest temperatures, the material becomes an
isotropic liquid where the motion of the molecules changes
yet again.
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Nematic
Simplest form is anematic liquid crystal
i.e. long-range
orientational orderbut no positionalorder
The preferred direction
is known as director
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NematicNematic
Despite the high degree of orientational order, nematic
phase as a whole is in disorder i.e. NO MACROSCOPIC
ORDER (orientation within a group is similar but not from one
group to another)
Structure of nematic phase can be altered in a number of ways.
E.g. electric or magnetic field or treatment of surfaces of the
sample container
Thus, possible to have microscopic order & macroscopic order Nematic liquid crystals are widely used in electro-optic display
devices
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Cholesteric
The first liquid crystal that was observed through a polarising
microscope is cholesteryl benzoate. Thus, CHOLESTERIC liquid
crystal OR chiral nematic liquid crystal
E.g. cholesteryl benzoate: LC @ 147C, isotropic @ 186C
Cholesteric liquid crystals have great potential uses as
- sensors
- Thermometer
- fashion fabrics that change colour with temperature
- display devices
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- In CHOLESTERIC phase,
there is orientational order &
no positional order, BUT,director is in HELICAL
ORDER.
The structure of cholestericdepends on the PITCH, the
distance over which thedirector makes onecomplete turn One pitch - several hundred
nanometers
Pitch is affected by:-
Temperature
Pressure
Electric & magnetic fields
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Smectic SMECTIC phase occurs at
temperature below nematic or
cholesteric
Molecules align themselvesapprox. parallel & tend to arrange
in layers
Not all positional order is
destroyed when a crystal meltsto form a smectic liquid crystal
Chiral smectic C liquid crystals are
useful in LCDS
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LIQUID CRYSTAL POLYMERS
Can form nematic, cholesteric, smectic
When liquid crystal polymers solidify, the liquid
crystal structure freeze in
This results in materials of high tensile
strength & in some cases unusual electro-
optical behaviour E.g. Kevlar aramid fibre bullet-proof vest &
airplane bodies (aromatic polyamide)
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Examples of phase changes
Cholesteryl myristate
solid smectic A
71C
cholesteric isotropic
79C 85C
4, 4-di-heptyloxyazoxybenxene
solid 74C 94C 124Csmectic C nematic isotropic
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Thermotropic vs Lyotropic
THERMOTROPIC
Absence of solvent
Rigid organic molecules
Depends on Temperature Structures:
Smectic
Nematic
Cholesteric
LYOTROPIC
In solvent
Surfactants
Depends on Temperature,
Concentration, salt, alcohol
Structures:
Lamellar
Hexagonal etc
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Structure formation in surfactant solution
micelle rod hexagonal
monolayer
bilayerReverse micelle
Formation of MICROEMULSION
REVERSE
HEXAGONAL
Oil/alcohol
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Effect of temperature and concentration on the
structure of lyotropic liquid crystals
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SURFACTANT VESICLES
[A] Phospholipids (e.g. lecithin) + H2O ---->
phospholipid vesicles or liposomes
[B] Liposomes + (long chain) stearylamine ------->
tve charge liposome (carriers for DNA)
[C] Liposomes + dicetyl phosphate -----
- ve charge liposome
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Vesicles
Bilayers that fold into a 3D structure
Vesicles form because they get rid of
the edges of bilayers, protecting the
hydrophobic chains from the water, but
they still allow for relatively small
layers.
Lipids found in biological membranesspontaneously form vesicles in
solution.
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Application of Liposomes
can encapsulate:
drugs,
proteins,
enzymes
administered intravenously, orally or intramuscularly
decrease toxicity
increase specificity of drug uptake enable slow release
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Problems with phospholipids
phospholipids undergo oxidative
degradation
handling & storage must be under nitrogen
expensive
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Formation of liquid crystals using surfactants
[A]Anionic
e.g. alkane sulfonates
[B] Cationic
e.g. hexadecyl trimethyl ammonium bromide
[C]Amphoterice.g. alkyl betaines
Due to toxicity of ionic surfactants, the vesicles are not used for
drug delivery
[D] Non-ionic
e.g. alcohol ethoxylates R-O-(CH2CH2O) m H
m: 2-20, R : mixed; alkyl group C8C18
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Non-ionic + cholesterol -> NIOSOMES
These vesicles prolong the circulation of entrapped
drug Properties depend on
1. Composition of bilayer
2. Method of production
e.g. cholesterol & single alkyl-chain non-ionic
surfactant with a glyceril head group
Niosomes
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Examples of niosome applications
Ketoconazole niosomes were prepared by using surfactant
(Tween 40 or 80), cholesterol and drug
Satturwar PM; Fulzele SV; Nande VS; Khandare, JN Indian Journal of
Pharmaceutical Sciences. 2002 Mar-Apr; 64(2): 155-8
Use for topical immunisation - Bovine serum albumin (BSA)loaded
niosomes composed of sorbitan monostearate/sorbitan trioleate
(Span 60/Span 85), cholesterol and stearylamine as constitutive
lipids
Sanyog Jain1, S. P. Vyas2, Journal of Pharmacy and Pharmacology Vol.57, No. 9, pages 1177 (2005)
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References
1. http://www.lci.kent.edu/lc.html#Description
2. http://liqcryst.chemie.uni-hamburg.de/lc_lc.php
3. http://www.glycoprojects.kimia.um.edu.my/website/Glyco/
(carbohydrate liquid crystal)
4. http://www.gla.ac.uk/~jmb17n/conacher.pdf(niosomes)
5. http://plc.cwru.edu/tutorial/enhanced/files/lc/phase/phase.ht
m
6. J Kreuter (ed.), Colloidal Drug Delivery Systems, Marcel
Dekker, New York (1994) Chapter 3&4
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http://plc.cwru.edu